Implantable devices are used for many indications including in the reproductive tract (e.g., uterine artery, fallopian occlusion), biliary implants and/or for peripheral and neurovasculature indications. For example, an aneurysm is a dilation of a blood vessel that poses a risk to health from the potential for rupture; clotting, or dissecting. Rupture of an aneurysm in the brain causes stroke, and rupture of an aneurysm in the abdomen causes shock. Cerebral aneurysms are usually detected in patients as the result of a seizure or hemorrhage and can result in significant morbidity or mortality.
There are a variety of materials and devices which have been used for treatment of peripheral and neurovascular aneurysms, including platinum and stainless steel microcoils, polyvinyl alcohol sponges (Ivalone), and other mechanical devices. For example, vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. One widely used vaso-occlusive device is a helical wire coil having windings that may be dimensioned to engage the walls of the vessels. (See, e.g., U.S. Pat. No. 4,994,069 to Ritchart et al.). Variations of such devices include polymeric coatings or attached polymeric filaments have also been described. See, e.g., U.S. Pat. Nos. 5,226,911; 5,935,145; 6,033,423; 6,280,457; 6,287,318; and 6,299,627. In addition, coil designs including stretch-resistant members that run through the lumen of the helical vaso-occlusive coil have also been described. See, e.g., U.S. Pat. Nos. 5,582,619; 5,833,705; 5,853,418; 6,004,338; 6,013,084; 6,179,857; and 6,193,728.
Coils have typically been placed at the desired site within the vasculature using a catheter and a pusher. The site is first accessed by the catheter (e.g., small diameter catheters such as those shown in U.S. Pat. Nos. 4,739,768 and 4,813,934). The catheter may be guided to the site through the use of guide-wires (see U.S. Pat. No. 4,884,579) or by flow-directed means such as balloons placed at the distal end of the catheter.
Once the site has been reached, the catheter lumen is cleared by removing the guidewire (if a guidewire has been used), and one or more coils are placed into the proximal open end of the catheter and advanced through the catheter with a pusher. Once the coil reaches the distal end of the catheter, it is discharged from the catheter by the pusher into the vascular site. However, there are concerns when discharging the coil from the distal end of the catheter. For example, the plunging action of the pusher and the coil can make it difficult to position the coil at the site in a controlled manner and with a fine degree of accuracy. Inaccurate placement of the coil can be problematic because once the coil has left the catheter, it is difficult to reposition or retrieve the coil.
Several techniques involving Interlocking Detachable Coils (IDCs), which incorporate mechanical release mechanisms and Guglielmi Detachable Coils (GDCs), which utilize electrolytically actuated release mechanisms, have been developed to enable more accurate placement of coils within a vessel.
Electrolytic coil detachment is disclosed in U.S. Pat. Nos. 5,122,136; 5,354,295; 6,620,152; 6,425,893; and 5,976,131, all to Guglielmi et al., describe electrolytically detachable embolic devices. U.S. Pat. No. 6,623,493 describes vaso-occlusive member assembly with multiple detaching points. U.S. Pat. Nos. 6,589,236 and 6,409,721 describe assemblies containing an electrolytically severable joint. The coil is bonded via a metal-to-metal joint to the distal end of the pusher. The pusher and coil are made of dissimilar metals. The coil-carrying pusher is advanced through the catheter to the site and a small electrical current is passed through the pusher-coil assembly. The current causes the joint between the pusher and the coil to be severed via electrolysis. The pusher may then be retracted leaving the detached coil at an exact position within the vessel. Since no significant mechanical force is applied to the coil during electrolytic detachment, highly accurate coil placement is readily achieved. In addition, the electric current may facilitate thrombus formation at the coil site. The disadvantage of this method is that the electrolytic release of the coil may require a period of time that may inhibit rapid detachment of the coil from the pusher.
There is a need to provide alternative mechanisms for delivering implants, such as embolic coils, that allow for both accurate positioning of the implantable device and rapid detachment from the delivery device.